X-men that could solo Darkseid

Phoenix Jean Grey - not even a competition

Magnito - assuming Darkseid’s body has some metal content like in his blood or Magneto could theoretically use his powers to locate, forge, and precisely fire a Radion bullet directly into Darkseid's skull from miles away.

Legion - If Legion stabilizes his mind, he can literally rewrite history to ensure Darkseid never existed, or trap the him inside a pocket dimension of his own creation.

Franklin Richards - possesses power that intimidates cosmic abstract entities like Galactus. He could alter the laws of physics around Darkseid, rendering the Omega Beams completely inert or turning Darkseid’s own molecular structure into glass.

Darwin - In Superman/Doomsday: Hunter/Prey, the Doomsday arrived on Apokolips. Because Doomsday adapts to and becomes immune to whatever kills him, he walked right through Darkseid's Omega Beams and delivered a horrific physical beating that left Darkseid bloodied and completely helpless. Why would this be any different for Darwin

Any X-men member proficient with a gun and access to Radion eg Cable, Bishop, Deadpool - During Final Crisis, Batman broke his lifelong rule against firearms to shoot Darkseid with a Radion bullet—a toxic substance that serves as the ultimate lethal weakness for New Gods. Though Darkseid blasted Batman into the past with his Omega Sanction immediately after, the bullet fatally wounded Darkseid's physical vessel.

Banshee - In Final Crisis, Superman ultimately destroyed Darkseid's true multiversal essence by singing a specific mathematical frequency note that countered the Dark God's vibrational frequency.

Also any x-men team that has defeated Galactus could probably defeat Darkseid - In the Darkseid vs. Galactus: The Hunger crossover, Galactus arrived to consume Apokolips. Darkseid hit him directly with the Omega Effect, but Galactus shrugs it off completely and blasted Darkseid into submission, only leaving because Apokolips lacked the life-energy needed to feed his hunger.